Let *can* be used inside a list comprehension, but it can also be its own statement. To be clear, in the code I posted above, I am not using list comprehensions. Documentation for the let statement exists on the wikibooks https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/The_OpenSCAD_Language#Let_Statement "[Note: Requires version 2016.XX] (ie a development version)" Hans On Sat, Feb 3, 2018 at 11:52 AM, George Hartzell <hartzell@alerce.com> wrote: > > It does not work in version `version 2015.03-3`, which is the stable > version installed via Homebrew Cask. > > It does work in the dev release that I manually downloaded, > `2017.12.23 (git 39823be1)`. > > This usage seems to be a variant of the list comprehension form, it's > documented [here][list-comp-let] without any caveats about what > release it will work in, although the top of that list comprehension > section states that it (list comprehensions in general?) requires > "2015.03". > > There's a comment in [this thread][let-thread] from 2016 that states > that `let` is only available in the dev releases. It also states that > "the wiki" has been fixed. > > Is there a doc bug in the User Manual? > > g. > > [let-thread]: http://forum.openscad.org/quot-Let-quot-deprecated-td17469.html > [list-comp-let]: https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/List_Comprehensions#let > > _______________________________________________ > OpenSCAD mailing list > Discuss@lists.openscad.org > http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org

for (...) {
  let(...) {
    ...
  }
}

for (i = [1:$children-1]) let($negative = true) {
  children(i);
}

for (i = [1:$children-1]) {
  let($negative = true) {
    children(i);
  }
}

Hans L writes: > Let *can* be used inside a list comprehension, but it can also be its > own statement. To be clear, in the code I posted above, I am not > using list comprehensions. > > Documentation for the let statement exists on the wikibooks > > https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/The_OpenSCAD_Language#Let_Statement > "[Note: Requires version 2016.XX] (ie a development version)" > [...] What that documents is a form like so: ```scad for (...) { let(...) { ... } } ``` What confused me a bit was that in the code you provided for me, the "for block" was simple enough that it didn't require braces: ```scad for (i = [1:$children-1]) let($negative = true) { children(i); } ``` This seems to function equivalently: ```scad for (i = [1:$children-1]) { let($negative = true) { children(i); } } ``` Is that correct? If so, then I believe I understand the subtleties. Thank you again! g.

for (...) {
  let(...) {
    ...
  }
}

for (i = [1:$children-1]) let($negative = true) {
  children(i);
}

for (i = [1:$children-1]) {
  let($negative = true) {
    children(i);
  }
}

Yes, precisely. Curly braces are only *required* when creating a "block" around *multiple* statements. If there is only a single statement under another, then the braces are optional. This is similar to the syntax found in most "c-style" languages (though I don't consider OpenSCAD to be c-style, it does share some simliarities such as this) You could even do the whole loop with no braces in this case, if you wanted. It is a matter of preference: for (i = [1:$children-1]) let($negative = true) children(i); On Sat, Feb 3, 2018 at 1:56 PM, George Hartzell <hartzell@alerce.com> wrote: > Hans L writes: > > Let *can* be used inside a list comprehension, but it can also be its > > own statement. To be clear, in the code I posted above, I am not > > using list comprehensions. > > > > Documentation for the let statement exists on the wikibooks > > > > https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/The_OpenSCAD_Language#Let_Statement > > "[Note: Requires version 2016.XX] (ie a development version)" > > [...] > > What that documents is a form like so: > > ```scad > for (...) { > let(...) { > ... > } > } > ``` > > What confused me a bit was that in the code you provided for me, the > "for block" was simple enough that it didn't require braces: > > ```scad > for (i = [1:$children-1]) let($negative = true) { > children(i); > } > ``` > > This seems to function equivalently: > > ```scad > for (i = [1:$children-1]) { > let($negative = true) { > children(i); > } > } > ``` > > Is that correct? If so, then I believe I understand the subtleties. > > Thank you again! > > g. > > _______________________________________________ > OpenSCAD mailing list > Discuss@lists.openscad.org > http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org